1. Field of the Invention
This invention relates to the fenceless control of animals, and more particularly, to the control of livestock utilizing a receiver attached to the animal that receives data identifying the location of the animal and administers appropriate control stimuli to the animal based on the location of the animal relative to the desired location.
2. Description of the Prior Art
Animal Confinement
Various conventional fencing systems are currently used to control the location of livestock. These systems include barrier fencing (such as barbed wire fencing) that physically blocks the movement of the animal and electric fencing that utilizes an electric shock to control the animal. The use of electric fencing has become more widespread because of its lower cost and ease of relocation.
Electric fencing has particular application in managed intensive grazing in which a large number of animals are confined to a smaller pasture area for a relatively short duration. Studies have shown that this higher stocking density followed by a longer period of no grazing yields significantly increased pasture productivity. This method more closely replicates the movement of an unrestrained herd of grazing animals and is more consistent with the evolutionary development of both grasses and grazing animals. Unfortunately, this method is labor intensive and requires substantial investment in electric fencing materials.
It is well established that animals respond to electrical stimuli, as evidenced by the effectiveness of electric fencing. A more recent development is the use of electrical stimulation via a stimulation device attached to the animal. Pet confinement systems have been developed that utilize an animal-attached receiver that applies an electrical shock when the animal approaches the proximity of a buried, current conducting, wire. Recent research has established that such a system also has application to livestock control.
U.S. Pat. No. 5,408,956, incorporated herein by reference as part of the disclosure hereof, describes a system in which animals wear small ear tag receivers that are activated when the animal enters an exclusion zone defined by stationary field transmitters. This system has particular application for locations in which traditional fencing is impractical and it is necessary to permanently exclude animals from sensitive areas.
Various methods have been developed for applying aural and electrical stimulus, including the ear tag described in U.S. Pat. No. 5,408,956 and the electronic nose clip described in U.S. Pat. No. 5,307,759, incorporated herein by reference as part of the disclosure hereof. Collar-mounted units are widely used in dog and other appropriate confinement applications. It is desirable to provide an audible signal prior to applying any electrical shock to allow the animal time to move and avoid the shock. In practice, the audible signal is generally sufficient to cause the desired animal movement.
Position Determination
Significant advancements have been made in the technology available to precisely determine the location of an object. The United States government has placed in operation a multiple satellite global positioning system ("GPS"). A GPS receiver receives signals from multiple satellites and calculates the position of the receiver based on the signal data. The method of operation of GPS systems is well known. For example, U.S. Pat. No. 5,379,224, incorporated herein by reference as part of the disclosure hereof, describes GPS system operation in detail. Even greater accuracy is possible with a "differential" GPS method that determines a correction factor based on the difference between the GPS-determined location of a fixed station and the actual known location of that station.
Many types of GPS receivers are available. Most include components to perform the processing functions necessary to convert the GPS satellite data into location information. Some receivers simply retransmit the data received from the GPS satellite to a central processing unit that converts that data into location information, in an effort to reduce the cost of the receiver components.